The phase change materials (PCM) are known to be materials that can change from a solid phase to a liquid phase or from a liquid phase to a solid phase, and during the phase change, a substantially amount of latent heat is absorbed or released. The most important feature of the phase change material is that when a great amount of latent heat is absorbed or released, the temperature of the phase change material system may be kept constant or within little variation. In the application of the phase change materials, it is usually to choose the phase change materials that have a large latent heat value and thus absorb/release more heat during the phase change, thereby obtaining better results. However, the phase change materials often leak or lose due to melting during the phase change when they are applied directly, thus reducing the life of the materials. Microencapsulation is a technique that coats on the surface of one material a trace amount of another material in a shell form. The use of the microencapsulation technique can prevent the phase change material from volume variation and leakage during melting. Furthermore, since the microencapsulated material has small particle size and large specific surface area, it also provides a large heat transfer area.
The encapsulation materials used for the microcapsules are mostly organic polymer materials, which have very low thermal conductivity and thus decrease the rate of heat transfer, though they can prevent the phase change materials from leaking.